Climate change is having a profound effect on the world around us. Many are well talked about like increased forest fire activity, heat waves, and droughts. But there are many subtler and equally disastrous changes afoot for worsening the biodiversity crisis. One of the lesser-known impacts is the effect rising temperatures has on the sex ratios of amphibians and reptiles. As the Earth's temperatures continue to fluctuate in extreme ways, it causes significant changes in the ratio of females to males being born for certain species. An out-of-sync ratio has obviously serious implications for the future of these species and the ecosystems they inhabit as reproduction is impacted.
In many species of amphibians, the sex of an individual is determined by the temperature of the environment during a critical period of development. This is known as Temperature-dependent Sex Determination (TSD). In species with TSD, warmer temperatures during development typically result in more females, while cooler temperatures result in more males. This process is essential for maintaining healthy populations of amphibians, but it is also highly sensitive to changes in temperature.
As global temperatures continue to rise, this delicate balance is being disrupted, leading to significant changes in the sex ratios of amphibians. In some cases, warmer temperatures are causing a disproportionate number of females to be born, which can lead to a lack of genetic diversity and reduce the overall fitness of the population. In other cases, cooler temperatures are resulting in a greater number of males, which can lead to competition for mates and further reduce genetic diversity.
One of the most well-studied examples of this phenomenon is the red-eyed treefrog (Agalychnis callidryas), a species found in Central and South America. Researchers have found that as temperatures increase, more females are being born, and the ratio of males to females is becoming increasingly imbalanced. Another example, a study of the European Common Frog (Rana temporaria) in the UK found that warmer temperatures resulted in a higher proportion of females. Similarly, a study of the Western Chorus Frog (Pseudacris triseriata) in Canada found that warmer temperatures resulted in fewer males. Similar effects are found on Sea Turtle populations and other reptiles.
In addition to TSD, some species have genetic sex determination, where sex is determined by the presence or absence of certain chromosomes. However, even in species with genetic sex determination, temperature can still play a role in determining sex. For example, researchers have found that exposure to warmer temperatures during development can cause male-typical gene expression patterns in female embryos of frogs.
Amphibians are a diverse group of cold-blooded animals that rely on their environment to regulate their body temperature. This makes them particularly vulnerable to changes in their habitat. Beyond sex effects, temperature fluctuations caused by climate change stand to devastate the population.
The effect of climate change are much more complicated than they may seem on the surface. As global temperatures continue to rise, the delicate balance of TSD is being disrupted, resulting in imbalanced sex ratios and reduced genetic diversity. This could have serious implications for the long-term survival of amphibian populations, which are already facing numerous threats, including habitat loss, pollution, and disease.
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